The brain is an inaccessible organ that cannot be examined by visual, palpatory or auscultatory methods currently used in clinical medicine. Although the suggestion of brain imaging was made early in the history of ultrasound for medical diagnostics, existing brain imaging techniques are non-ultrasonic in their nature. The most popular brain imaging techniques are Magnetic Resonance Imaging (MRI), and Position Emission Tomography (PET). The equipments providing such imaging are extremely expensive. Furthermore, PET requires chemical radioactive tracers, and MRI works with a strong magnetic field. Both techniques need a long integration time for metabolic activity or structure measurements (e.g. about 45 min. for PET, and 2 min. for MRI), so they are incapable of showing real time live pictures of the human brain.
There are several real time, two-dimensional color ultrasonic scanning techniques currently used in clinical diagnosis. The most popular are Color M-Mode Scanning and Color Doppler. However, they are not applicable for brain imaging, and also suffer some disadvantages.
The image in Color M-mode Scan is interpreted by pattern recognition, but it does not correlate with the usual two dimensional structure anatomy as depicted in real time imaging. The detected motion in the lateral direction is not portrayed because of the limited field of view. Furthermore, this scanning is based on two-dimensional extrapolation of geometric shapes based on one dimensional measurement, which introduces an error. This scanner is mainly used in echocardiology.
The major disadvantages of duplex scanning in Color Doppler are related to the fact that the flow is not evaluated simultaneously throughout the field of view but rather is sampled at a particular location as selected by the sonographer. To establish the region flow pattern, an FFT analysis must be performed at multiple sites throughout the vessel, which requires precise positioning of the sampling volume; color coding is based on the average, rather than the peak Doppler shift; progressing across the field of view, a vessel with constant flow is depicted with different colors and so on. The highest priority for such a scanner is the observation of arterial and venous flow. Furthermore, such techniques are based on a velocity detection, so they are not able to measure small amplitude variations, and cannot provide imaging through the skull.
It is among the objects of the present invention to provide improvement over prior art ultrasonic techniques for imaging the body, and which can be used for practical imaging and diagnosis of the brain.